In the technical field of liquid crystal display, the liquid crystal display (LCD) does not emit light, and a backlight source is usually arranged on a hack surface of the LCD to implement image display.
Backlight sources may be divided into a direct-down type and an edge type according to positions of the light sources in backboards. The edge type backlight source has the characteristic that the light source is on an edge of the backboard, light emitted by the light source directly enters a light guide plate and the light guide plate causes the light from the light source to form an area light source covering the whole backboard. The direct-down type backlight source has the characteristic that the light source is laid on the whole backboard and light from the light source is emitted to an LCD through the light guide plate arranged in the above. In order to achieve a relatively better light mixing effect, the direct-down type backlight source requires a relatively longer light mixing distance, i.e. a relatively longer distance between the light source and the light guide plate. However, because the edge type backlight source has no requirement on the light mixing distance, the edge type backlight source is widely used due to its characteristics of lightness, thinness, low power consumption and the like.